In cognitive radio techniques, secondary users (CR transceivers) dynamically change transmit and receive parameters so that their signals do not interfere with signals of primary users (PU transceivers). Conventionally, cognitive radios consider radio frequency spectrum utilization, user behavior, and network state. Cognitive radios are considered in the IEEE 802.15, IEEE 802.19, and IEEE 802.22 standards. Conventionally, cognitive radio techniques conduct one-dimensional spectrum sensing by periodically scanning only the frequency domain to locate unused frequency bands (“spectrum holes”). The unused frequency bands can then be used for CR to transmit signals that do not interfere with the signals of the PUs.
To obtain accurate result, a duration Ts(f) is used by the CR to sense the spectrum at the frequency band f. The sensing can be conducted by directly measuring the of PU signals (power-based sensing), or by analyzing statistics of the signals transmitted by PUs, (intelligent sensing).
Spectrum sensing can be categorized as focal sensing, and cooperative sensing. Local sensing is performed by a single CR. Cooperative sensing is performed by multiple CRs that share results. The performance of local sensing can be suboptimal due to shadowing and fading. Consequently, “hidden” PUs can exist because a single CR cannot detect the existence of all PUs that can receive interfering signals. In addition, locating a large number of unused frequency bands is better performed cooperatively.
In cooperative spectrum sensing, associated CRs can exchange local sensing results, so that a cognitive network obtains an accurate estimate of unused frequency band, or even, locations of the PUs.